Air traffic control utilizing rotating radial signals

ABSTRACT

Air traffic is controlled to follow azimuthally rotating radial signals, from an off-airport terminal omnirange station, sweeping over an air-port in a direction and at a speed suitable for approach to landing. Dual omnirange stations flanking the airport may be used similarly for control of traffic to respective dual runways or for control of departure after takeoff as well as approach to landing.

[ 1 May 1, 1973 United States Patent n 1 Kurkjian 2,844,817 7/l958Green........................... .343/l 12 TC [54] AIR TRAFFIC CONTROLUTILIZING ROTATING RADIAL SIGNALS Primary Examiner-Carl D. Quarforth[76] Inventor: lhig Kurkjlan, RD. 1, Malvern, Pa.

Attorney-McClure, Weiser & Millman [22] Filed: Mar. 27, 1970 [21] Appl.No.: 23,344

station, sweeping over an air-port in a direction and at [52] US.CI........343/ll2 TC, 343/112 CA, 343/106 [51] Int.

a speed suitable for approach to landing. Dual om- QGMS 3/02 nirangestations flanking the airport may be used [58] Field of Search 12 TC,112 CA,

similarly for control of traffic to respective dual runways or forcontrol of departure after takeoff as well as approach to landing.

16 Claims, 4 Drawing Figures [56] References Cited UNITED STATES PATENTS2,252,083 8/1941 Luck 12 TC Patented May 1, 1973 3,731,312

3 Sheets-Sheet 1 wmvme HAIG KURKJIAN J M L vwv ATTOP/VEYJ'.

Patented May 1, 1973 3,731,312

3 Sheets-Sheet 2 M a a; Wmfu A T7'OR/VEYJ.

Patented May 1, 1973 3 Shets=Shet 3 M/VE/VTOK. K U R K J IA N AIRTRAFFIC CONTROL UTILIZING ROTATING RADIAL SIGNALS This invention relatesto a system for control of air traffic through use of radio signals.

A principal existing aid to navigation of aircraft is the omnirangeradio station; or VOR, i.e., very high frequency omnidirectional range.VOR signals are interpreted conventionally as radials radiatingtherefrom (viewed in plan) like the spokes of a horizontal wheelconcentric with the station. Such radial signals are azimuthallycharacteristic} being distinguishable from one anotheraccording to theirdirection from the station. Notwithstanding suchuse of the term rangethe azimuthally characteristic signals from such a station provideinformation about direction only, rather than distance. Conventionaltransmitters of DME or TACAN type may be present at the same station forthe purpose of transmitting signals characterizable by appropriatereceiving equipment in terms of distance, speed, or time to station.Such receivers are much less common in aircraft than are navigationreceivers for VOR signals.

Congestion is becoming a problem in high-density air traffic terminalareas, including routes for approach to landing and for departure aftertakeoff as well as runways and adjacent ground facilities of airports.As is obvious, an airport is a bottleneck for air traffic, and theproblem is aggravated not only by traffic density but also by diverseperformance characteristics of the aircraft being funneled into and outof the airport and by reason of operation of the aircraft under diverseflight rules, such as what are now known as visual flight rules (VFR)and instrument flight rules (IFR). Many proposals have been made forcoping with the air terminal traffic problem, but there has been nosatisfactory solution that is simultaneously easy for controllers toadminister and for pilots to follow, that also poses essentially nosafety problem, and that can be accomplished without requiringadditional navigation equipment in the aircraft.

A primary object of the present invention is provision of a system ofterminal air traffic control for which retraining of controllers andpilots is minimized.

Another object is provision of such a system in which separation ofterminal traffic by reason of differences in aircraft performance isassured.

A further object is provision of such a system operable by use ofnavigation receivers in most common use.

Other objects of this invention, together with means and methods forattaining the various objects, will be apparent from the followingdescription and the accompanying diagrams.

FIG. 1 is a schematic diagram of a first embodiment of air trafficcontrol system according to the present invention;

FIG. 2 is a perspective view of a ground transmitting station of radiosignals useful according to the invention;

FIG. 3 is a schematic diagram of a second embodiment of air trafi'iccontrol system according to this invention; and

FIG. 4 is a schematic diagram of a third embodiment of air trafficcontrol system according to the invention.

In general, the objects of the present invention are attained, in asystem of aircraft traffic control in terminal airspace wherein anairport has nearby an omnirange station adapted to broadcast azimuthallycharacteristic radial signals, by imparting an azimuthal rotation to thesignals to sweep over the airport in a direction and at a speed suitablefor air traffic approach to landing. Approaching aircraft are controlledto orbit the station on a designated rotating radial until entering alanding pattern, which itself may be entirely conventional. Departingaircraft may be constrained similarly to follow designated rotatingradials for at least part of their departure paths.

FIG. 1 shows in schematic plan a terminal area containing airport 10with runways (shown fragmentarily and greatly enlarged) 9 and 17. Fanmarker 12 is shown superimposed upon centerline 11 of runway 9 left ofthe intersection, and localizer beam 14 extends along and flanking thatcenterline. Also superimposed in this view is a gridwork of radials R RR R,,R,,,,, R R R radiating from terminal omnirange station 20.Successive distance circles 22, 23, 24 are concentric therewith, and theairport is distant from the station by the radius of circle 22.

Additionally superimposed (in broken lines) on FIG. 1 are approach path26 of small aircraft 25 and approach path 28 of larger aircraft 27.Entering from the upper right, the respective aircraft orbit the stationthrough approximately semicircular arcs, smaller for the light aircraftand larger for the heavier aircraft, until nearing or reaching runway 9.Aircraft 27 follows an instrument landing pattern straight in ontorunway 9, and aircraft 25 is diverted into a right-hand traffic patternto land on runway 17. Departure paths 26 (from runway 17) and 28', (fromrunway 9) of the respective aircraft also are shown.

Radials R R R,,, R R R R R are shown ten degrees of arc apart and aredesignated successively herein by R plus each of eighteen successivesingle-letter subscripts and a like number of doubleletter subscripts.The designation begins at the first radial clockwise from the radialextension of arrow 29 and progresses from there; R, is the reciprocal of(i.e., degrees from) radial R and R is the reciprocal of R etc. Suchsubscript designation is a shorthand for conventional numericaldesignation, according to which these 36 radials would be designated010, 020, 350,- 360". Thus, if the radials were stationary, as in thecase of a conventional omnirange station, each radial would designate anazimuthal direction from the station itself and would be so interpretedby an aircraft navigation receiver. Such stations are well known in theart and do not require extended description here.

In summary, a conventional type of VOR station comprises radiotransmitting equipment adapted to transmit azimuthally characteristicsignals. One way in which this is done is by producing a VHF carrier(e.g., in the 108 to 118 megahertz band) modulated by both a referencelow-frequency signal (e.g., 30 hertz) transmitted equally in allazimuthal directions and by a similar but directional signal transmittedwith azimuthally phase-distinguishable characteristics. This is doneconveniently by amplitude-modulating the carrier directly with thevariable-phase signal and separately with asubcarrier (e.g., about 10kilohertz, perhaps 9960 hertz) frequency-modulated with the referencesignal. The latter is transmitted by a centrally located antenna free ofdirectional characteristics, and

the former is transmitted by antennas (usually four in number) equallyspaced about the central antenna, thereby rendering it azimuthallycharacteristic. Also included in the amplitude modulation of the carrieris a station identifier, which may be at voice frequency or coded tonein the audio range,

The aircraft navigation receiver simply detects the low-frequencyvariable-phase signal (as well as the station identifier) and thesub-carrier, sends the subcarn'er to an FM detector to obtain thereference signal, then compares the variable-phase and reference signalsin a phase-detector to ascertain on what radial from the station theaircraft is located. The resultant information is presented on aconventional instrument (called an omnibearing selector or OBS, whichmay be incorporated in a more comprehensive instrument, such as a flightdirector) having a rotatable azimuth (radial) scale and a deflectableneedle that centers when the radial indicated on the azimuth scale isthe radial on which the aircraft is located. The needle deflects to oneside or the other when the aircraft intercepts a radial other than thatindicated on the scale, except for the reciprocal radial.

FIG. 2 shows an omnirange station of the type described briefly abovemodified for use according to this invention by rotation of the antennaassembly. Station comprises a transmitter house or shack 30 having ontop thereof flat circular roof 35, which provides a reflecting plane,surmounted by frustoconical tower 36 on top of which is cylindricalhousing 37 for the antennas: central reference signal antenna 31 andsurrounding phase-signal antennas 34a, b, c, d. Whereas the antennahousing is conventionally stationary, in the practice of the presentinvention the antenna housing is rotated at constant speed about itsvertical axis as indicated by the adjacent arrow. Suitable speed ofrotation depends upon the distance between station and airport butusually will be on the order of tens of degrees per minute, e g., 20 permin.

Rotation of the antenna housing causes like rotation of the azimuthallycharacteristic signals and the associated radials. Such rotation isindicated in FIG. 1 by the arcuate arrow terminated by an undesignatedfragmentary radial line, appearing at the upper right of the view. Itwill be understood that the designation of radials at ten-degreeintervals is merely exemplary and that the station emits an infinitudeof radials; OBS scales usually are marked at five-degree intervalsalthough readable to about a degree. In the actual practice of thisinvention intervals of five or ten degrees will suffice, as will beapparent from the following operational description.

Aircraft approaching the station will be controlled initially, when theradials are rotating counterclockwise as shown, to approach from agenerally northern direction, such as indicated by paths 26 and 28 orarrows 36, 38, and 39. Such control may be by voice transmission, asfrom an approach controller to the aircraft pilot or as an addendum tothe station identifier of the terminal omnirange station, for example.The aircraft so approaches the station until reaching a radius therefromat which the speed of the aircraft equals the rotational speed of theradials at such radius, whereupon the aircraft orbits the station on aparticular radial, which usually will be designated by a controller,until entering a landing pattern. This procedure may involvecommunication to and from controller and pilot. If desired, theprocedure may be automated partially or wholly, especially where theaircraft and the station have DME (distance-measuring equipment)capability, by means of automatic-pilot radio equipment in the aircraftadapted to couple to the designated radial and to maintain the desiredorbiting distance from the station, as will be readily understood bythose skilled in the art. The controller, whether human or otherwise,may monitor the performance by radar observation of the aircraft.

When a human pilot has the responsibility for proper approach procedure(and it is anticipated that the ultimate responsibility will be his forthe foreseeable future, regardless of the degree of automation providedto aid such navigation) he can check his progress readily by observationof the OBS needle, with the designated radial dialed onto the azimuthscale. If the aircraft speed exceeds the speed of the radial at theorbiting distance, the needle will deflect o the left of center,indicating that the aircraft should turn left somewhat, whereupon theaircraft can intercept the radial closer to the station, at a radiuswhere its linear speed is less. Contrariwise, if the needle deflects tothe right of center. Of course, aircraft speed may be adjusted inaddition to or sometimes instead of making directional corrections.

After partial orbiting of the station on the designated radial theaircraft is directed into a suitable landingpattern. Thus aircraft 25following path 26 orbits on such radial at a speed of ninety or ahundred knots, for example, just inside distance circle 22, which may beat about 6 miles (nautical) from the station. This aircraft is assumedto be operating VFR, so the airport will become visible as the aircraftswings around toward the east, whereupon the controller can direct itreadily into a right-hand traffic pattern for runway 17. Aircraft 27,however, which is operating lFR (even if actual conditions aresatisfactory for VFR operation) follows path 28 and orbits on itsdesignated radial between distance circles 23 and 24 (at respectiveradii of about seven and eight miles, for example) as at a speed ofabout or 60 knots, until intercepting localizer beam 14. Then aircraft27 may complete an otherwise conventional instrument approach straightin to runway 9, following the localizer beam (with or without glideslope), passing over fan marker 12, which may be an outer, middle, orinner marker, and disregarding its position relative to the previouslydesignated radial. Alternatively, in further accord with this invention,adherence to such radial may be continued while on the localizer beam,requiring reduction in ground speed because the radius from the stationis being reduced. Such speed reduction usually will induce descent alongan appropriate glide path in conformity with or substitution for thatprovided by glide slope equipment.

It will be understood, of course, that at the crossover of paths 26 and28 of respective aircraft 25 and 27, aircraft 25 will be at a loweraltitude than aircraft 27, both normally and according to approachprocedure of the present invention. Also, of course, aircraft will becontrolled to enter the approach pattern at appropriate in tervals tointercept and orbit on radials suitably spaced from one another in theinterest of safety. Orbiting for one or more complete turns ondesignated radials may be employed to shuttle aircraft safely fromhigher a1- titudes to suitable approach altitudes.

Departures are handled either similarly tomor somewhat differently frornapproaches in this first embodiment of the invention, wherein only asingle terminal VOR is used, depending chiefly upon aircraft performancecharacteristics. A relatively high-performance aircraft, such as 27, canaccelerate sufficiently to take off from runway 9 and initially follow'adesignated radial, which requires substantial increase in ground speedwith increasing distance from the VCR station, after which the aircraftmakes a half-right turn out to the southeast, as indicated by path 28'.Lowerperformance aircraft 25 takes off from runway 17 and immediatelymakes a half-left turn out to the southeast, as indicated by path 26.Because of the greater speed and rate of climb of aircraft 27, there isno intersecting or overlapping of their respective departure paths.

Thus, where only a single terminal omnirange station is used in thevicinity of an airport, approaches preferably are confined to thestation side of the airport and departures to the opposite side. Ofcourse,'aircraft approaching from the opposite side or departing fromthe same side are expected to maneuver appropriately when beyond theterminal area so as to avoid interference. Usually there is no necessityto use an approach radius of more than about ten miles, corresponding toa speed exceeding two hundred knots at a radial rotation of 20 perminute, and a radius of from to miles would clear departures as well.The direction of radial rotation may be reversed, if desired, as byreason of change in wind direction, with reversal in the trafficpatterns, as will be readily understood. The direction of radialrotation can be broadcast conveniently along with the station identifieras well as by I controllers or otherwise.

More sophisticated control of departing, as well as approaching,aircraft is provided according to another embodiment of the presentinvention, illustrated in Fig. 3. In this second embodiment, in whichairport 10 and omnirange station 20 are shown as before, anotheromnirange station is added: station 20' is located at preferably thesame distance from the airport as station 20 but on the opposite sidetherefrom. In the illustration, stations 20 and 20' flank the airport,and centerline 11 of runway 9 is a perpendicular bisector of thestraight line interconnecting the two stations (corresponding torespective radials R and R, at the moment of rotation shown in FIG'. 3).Reference characters to designate certain of the radials, especiallymost of those meeting over the station, are omitted in the interest ofclarity. The radials from station 20", are designated similarly to thosefrom station 20 but, with the R primed, thus: R,,, R,,, R,,, R',.,R',,,,, R' 12' R,,.. If it is inconvenient to locate both stations atidentical distances from the airport, the rate of rotation of thefurther station preferably will be adjusted suffrciently slower than therate of rotation of the radials of the nearer stationso that the groundspeed of the radials from both stations are synchronized to be identicalat the airport. The frequency upon which station 20 broadcasts isdifferent, of course, from the frequency of station 20.

1 description, which will not be repeated here l-Iowever,

departing'aircraft are controlled further by reference to the rotatingradials of omnirange station 20, as follows. Aircraft 2 5,takes off fromrunway 17 as before but now proceeding generally toward station '20,where the speed of the'radials overthe ground is less. Thus, it issimple for aircraft 25 to .make'a left turn out onto a designated radialon which it can orbit the station at climb-out speed, such as aboutknots When the controller is satisfied that the aircraft has "sqproceeded to a suitable altitude and direction, he then releases it fromthe constraint of orbiting on that radi'aL a's'at point 41 on itsdeparture path (here designated as 26" to distinguish it from path 26'of FIG. 1), whereupon it maneuvers to an enroute course dependent uponits destination.

Similarly, in FIG. 3 faster aircraft 27 makes a left turn out onto aradial with larger radius, such as at a speed approaching 200 knots, andorbits the station through an appropriate are (here shown as almost asemicircle) before being released from such constraint. It will beunderstood that at the indicated cross-over of departure paths 26" and28" aircraft 27 will have climbed to a'higher altitude than aircraft 25,so that a safe separation is assured.

In a departing aircraft the OBS will show a left needle if the aircraftis traveling faster than the designated radial, in which event turningleft slightly will increase the radius to a faster radial ground speed,thereby correcting in the same manner as a pilot corrects the courseduring enroute navigation. Conversely, turning more to the right willcorrect for aircraft speed deficiency. Thus, the human pilot need notget acquainted with any new equipment or learn any new navigationtechnique for either approaches or departures according to thisinvention Where DME is used, as is desirable, observation-of thedistance from the station, as presented on the DME indicator in theaircraft, enables the pilot to make appropriate adjustments (as inpower, for example) to make certain that the aircraft is maintaining thedesignated orbiting radius. This also may be automated, if desired, byappropriate setting of an autopilot having suitable interconnection of acourse coupler and an orbiting mode.

A third embodiment of this invention, shown in FIG. 4, is for use withdual parallel runways, such as runway 9L (left) and 9R (right) ofairport 40 shown substituted for airport 10 between omnirange stations,20 and 20'. It should be remembered that the showing of the. runways notonlyis way out of scale compared to the distance from the stations butalso that the runway width isexaggerated with respect to the lateralspacing between the runways, which is many (e.g., 10 to 20) times therunway width. Only runway 9R is shown with a localizer.beam,"aswhenrunway 9Lwill be used only for VFR operations. However, where traffie isparticularly heavy and adequate lateral separation is available, bothrunways maybe equipped with instrument landing systems, includinglocalizer beams (on different frequencies) as will be readilyunderstood.

In. this embodiment, aircraft 45 in the upper left (northwest) quadrantapproaches on path 46, orbiting on a designated radial, and lands onrunway 9L. After subsequently taking off on the same runway, it departsto the upper right, with or without a necessarily brief period oforbiting (as shown) via departure path 46. Similarly, aircraft 47approaches at the lower left, orbits, and lands on runway 9R, afterwhich it takes off on that runway and departs via path 48', with orwithout a brief period of orbiting. All aircraft follow both landing andtakeoff traffic patterns conforming to the runway position, i.e., lefttraffic patterns to and from runway 9L, and right traffic patterns toand from runway 9R. In this regard there is less freedom of action thanin the previous embodiments, but that is generally true in operationsinvolving dual runways because of the parallellism in directions oflanding (and taking off). Arrows 49 and 49' mark radial rotation anddesignation from stations 20 and 20 (as arrows 29 and 29' did in FIG.3).

It will be understood that in all embodiments of the invention thedirection of radial rotation may be reversed if desired, as because ofchange wind direction, for example. The fact of reversal, or of intended reversal, may be broadcast as an addendum to station identifieror otherwise.

Advantages of convenience and safety accruing in the practice of thisinvention have been mentioned above and are apparent. An added benefitis economic, inasmuch as no change in aircraft navigation equipment isrequired; the addition of terminal omnirange stations is compensated forby resulting simplification of controller work load. Although explainedin large part with reference to operation by human controllers andpilots, adaptation to an increasing degree of automation is inherent andwill be readily appreciated by those skilled in the art. Thus,computerized control may replace human control to an unlimited extentwhile using essentially the same control system.

The present invention is also adapted for use with Doppler omnirangeequipment, wherein the variable phase signal is modulated onto the 10kilohertz subcarrier, contrary to the conventional VOR described above,by appropriate alteration in the rotating distribution system to themultiple (such as 50) antennas concentric with the single referencesignal antenna.

Other modifications may be made, as by addition, combination, orsubdivision of parts or steps, while retaining some or all of theadvantages and benefits of this invention. The invention itself isdefined in the following claims.

I claim:

1. in aircraft traffic control in terminal airspace wherein an airportis within range of an omnirange station located off the airport andadapted to broadcast azimuthally characteristic radial signals, theimprovement comprising imparting an azimuthal rotation to the signals tosweep over the airport in a direction and at a speed suitable for airtraffic approach to landing.

2. Aircraft traffic control according to claim 1, including the step ofdesignating a certain rotating radial upon which an approaching aircraftis to orbit the omnirange station until entering a landing pattern.

3. Aircraft traffic control according to claim 2 wherein a portion ofthe landing pattern is provided by a localizer beam aligned with thedesired landing location for intersection by successive radial signals.

4. Aircraft trafiic control according to claim 1, wherein the distanceof the omnirange station from the airport is about 5 to 10 miles, andthe rate of rotation of the radial signals is about 20 per minute.

5. Aircraft traffic control according to claim 4, wherein landingaircraft are controlled to make a left traffic entry when the directionof rotation of the radial signals is counter-clockwise, and a righttraffic entry when the direction of rotation is clockwise, as viewed inplan.

6. Aircraft traffic control for terminal airspace, comprisingbroadcasting azimuthally characteristic radial signals sweepingazimuthally at constant velocity over a nearby airport in a directionand at a speed suitable for approach to landing of aircraft, designatinga certain radial to be followed by a given approaching aircraft, andcontrolling the aircraft to orbit the omnirange station on that radialuntil entering a conventional landing pattern.

7. Aircraft traffic control according to claim 6, including the step ofdesignating a certain altitude to be followed by the given approachingaircraft during the orbiting of the station by the aircraft.

8. Aircraft traffic control according to claim 6, including the steps ofdirecting IF R traffic to land essentially tangentially to the radialand directing VF R traffic to land in a more nearly radial direction.

9. Aircraft traffic control according to claim 6, including the step ofproviding to the aircraft an indication of any deviation of the aircraftfrom the designated radial.

10. Aircraft traffic control for terminal airspace, comprisingbroadcasting azimuthally characteristic signals from, a pair ofomnirange stations flanking an airport and counter-rotating the radialsignals from the respective signals azimuthally in opposite directionssynchronously.

11. Aircraft traffic control according to claim 10, including the stepsof controlling approaching aircraft by use of the signals from one ofthe stations and controlling departing aircraft by use of the signalsfrom. the other station.

12. Aircraft traffic control according to claim ll, including the stepof constraining approaching aircraft to orbit the first station on adesignated radial thereof until entering the landing pattern andconstraining de parting aircraft to orbit the second station on adesignated radial thereof until leaving the departure pattern.

13. Aircraft traffic control according to claim 12, wherein theapproaching aircraft and departing aircraft are constrained to followoppositely directed traffic patterns.

14. Aircraft traffic control according to claim 11, wherein dualparallel runways are used, including the steps of controlling aircraftapproaching and departing one of the runways by use of the signals fromone of the stations and controlling aircraft approaching and departingthe other runway by use of signals from the other station.

15. Aircraft traffic control according to claim 14, including the stepsof constraining aircraft approaching for landing on the first runway toorbit the first station on a designated radial thereof, and constrainingaircraft approaching for landing on the second runway to orbit

1. In aircraft traffic control in terminal airspace wherein an airportis within range of an omnirange station located off the airport andadapted to broadcast azimuthally characteristic radial signals, theimprovement comprising imparting an azimuthal rotation to the signals tosweep over the airport in a direction and at a speed suitable for airtraffic approach to landing.
 2. Aircraft traffic control according toclaim 1, including the step of designating a certain rotating radialupon which an approaching aircraft is to orbit the omnirange stationuntil entering a landing pattern.
 3. Aircraft traffic control accordingto claim 2 wherein a portion of the landing pattern is provided by alocalizer beam aligned with the desired landing location forintersection by successive radial signals.
 4. Aircraft traffic controlaccording to claim 1, wherein the distance of the omnirange station fromthe airport is about 5 to 10 miles, and the rate of rotation of theradial signals is about 20* per minute.
 5. Aircraft traffic controlaccording to claim 4, wherein landing aircraft are controlled to make aleft traffic entry when the direction of rotation of the radial signalsis counter-clockwise, and a right traffic entry when the direction ofrotation is clockwise, as viewed in plan.
 6. Aircraft traffic controlfor terminal airspace, comprising broadcasting azimuthallycharacteristic radial signals sweeping azimuthally at constant velocityover a nearby airport in a direction and at a speed suitable forapproach to landing of aircraft, designating a certain radial to befollowed by a given approaching aircraft, and controlling the aircraftto orbit the omnirange station on that radial until entering aconventional landing pattern.
 7. Aircraft traffic control according toclaim 6, including the step of designating a certain altitude to befollowed by the given approaching aircraft during the orbiting of thestation by the aircraft.
 8. Aircraft traffic control according to claim6, including the steps of directing IFR traffic to land essentiallytangentially to the radial and directing VFR traffic to land in a morenearly radial direction.
 9. Aircraft traffic control according to claim6, including the step of providing to the aircraft an indication of anydeviation of the aircraft from the designated radial.
 10. Aircrafttraffic control for terminal airspace, comprising broadcastingazimuthally characteristic signals from a pair of omnirange stationsflanking an airport and counter-rotating the radial signals from therespective signals azimuthally in opposite directions synchronously. 11.Aircraft traffic control according to claim 10, including the steps ofcontrolling approaching aircraft by use of the signals from one of thestations and controlling departing aircraft by use of the signals fromthe other station.
 12. Aircraft traffic control according to claim 11,including the step of constraining approaching aircraft to orbit thefirst station on a designated radial thereof until entering the landingpattern and constraining departing aircraft to orbit the second stationon a designated radial thereof until leaving the departure pattern. 13.Aircraft traffic control according to claim 12, wherein the approachingaircraft and departing aircraft are constrained to follow oppositelydirected traffic patterns.
 14. Aircraft traffic control according toclaim 11, wherein dual parallel runways are used, including the steps ofcontrolling aircraft approaching and departing one of the runways by useof the signals from one of the stations and controlling aircraftapproaching and departing the othEr runway by use of signals from theother station.
 15. Aircraft traffic control according to claim 14,including the steps of constraining aircraft approaching for landing onthe first runway to orbit the first station on a designated radialthereof, and constraining aircraft approaching for landing on the secondrunway to orbit the second station on a designated radial thereof,before entering a landing pattern.
 16. Aircraft traffic controlaccording to claim 15, wherein aircraft approaching and departing viaeach runway are constrained to follow oppositely directed trafficpatterns.